I see SQL as a query language, used to store and retrieve data. However, there are now many versions of new words with different features. Now I am using SQL to manage school data. So now which version should I use? Please give me some advice.
ANSI-SQL is the international standard.
Microsoft has implemented that, and extended the language as T-SQL. Oracle has done the same thing as PL-SQL. Each RDMS has implemented various extensions to the original language.
The RDMS you choose determines what dialect of SQL is available to you.
Choosing an RDMS is probably more dependent upon costs, time to learn the RDMS, and your infrastructure.
When you say "there are now many versions of new words with different features", what specifically are you referring to?
The word SELECT is universal to all dialects. However, TRY_CONVERT is specific to T-SQL (Microsoft)